The present invention relates to a highly absorbent nonwoven web formed from readily available nonwoven materials and a polyelectrolyte super-absorbent polymer.
Absorbent sheet materials have been obtained through the incorporation of super-absorbent polymers onto various carrier substrates. In most of these materials, the carrier substrate is used to provide the mechanical support for the absorbent components which have little or no mechanical stability per se. Approaches to providing sorbent/carrier composites have varied, often involving the combination of film or particulate forms of super-absorbent polymer in sandwich or laminate types of construction. (See U.S. Pat. Nos. 4,008,353 and 4,190,562).
In some of these constructions, highly localized concentrations of super-absorbent polymers are layered between two substrates with at least one side of the final structure being water permeable. Other constructions are known in which the sorbent is coated onto the top or bottom or both sides of a nonwoven web. While these composites include substantial amounts of super-absorbent materials, they do, nonetheless, have inherent drawbacks which become evident in particular applications. Thus, where the need for rapid uptake of liquid is an essential performance criterion, especially where the super-absorbent polymers are the primary absorbent constituent, the highly localized (planar) concentration of the super-absorbent polymers causes these composites to suffer from the effects of the gel blocking phenomenon of super-absorbent polymers. Super-absorbent polymers, by their nature, swell but do not dissolve upon contact with water. It is this mechanism that allows these materials to imbibe and retain large amounts of liquids. While super-absorbent polymers are excellent for the containment of water (swelling occurs through osmotic effects), liquid transport through the gel occurs primarily by diffusion and is necessarily limited in rate. If several layers of planar-dispersed super-absorbent polymer are used, then the gel layer produced upon wetting of the surface layer closest to the liquid source, will act essentially as a liquid barrier. These effects are widely recognized and in some instances can provide desirable results. U.S. Pat. No. 3,888,256 discloses a diaper construction in which a particulate swelling substance is arranged in one of the layers closest to the baby's skin. The particles are distributed such that: their spacing allows for an initial passage of liquid (urine), but as the particles swell upon wetting, they close off the open portion of the web and ultimately provide a barrier to back-flow of liquid.
When a barrier effect is not desirable, which would be the case where the super-absorbent polymer is the primary absorbent component, then alternate dispersion schemes must be utilized. Methods for producing near homogeneous dispersions of super-absorbent polymers in open network systems have involved both liquid and air carrier methods for incorporation of the water swellable but water insoluble super-absorbent polymers into the open network. In the liquid carrier method, swollen super-absorbent polymer particles in an aqueous suspension are deposited onto the substrate surface and the liquid carrier evaporated to produce an anchored super-absorbent polymer composite. (U.S. Pat. Nos. 4,235,235 and 3,686,024).
Swollen gel particles at even moderate concentrations in an aqueous system are very viscous suspensions and are inherently difficult to handle from a processing standpoint. If lower suspension concentrations are used to reduce the viscosity effects, then a need to remove proportionately larger amounts of liquid carrier becomes necessary in an evaporation step. Alternate methods of controlled deposition utilize air as the super-absorbent polymer carrier (U.S. Pat. No. 4,429,001). While this method overcomes many of the process related drawbacks of wet deposition, these composites retain the particulate super-absorbent polymer in the web through mechanical entrapment thereby presenting an opportunity for some loss (by dusting out) of the super-absorbent polymer component.